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update on my 2nd San Mai attempt.


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Keep at it.  Hard to say what went wrong but I'd guess you're not quite getting it hot enough.  Are you using flux when welding?

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I am. I think you're right about not getting hot enough. I'm thinking that my single burner foundry furnace turned forge may not get hot enough. I do have a few more burners. I've been considering building a proper forge.

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I can't see why that wouldn't get hot enough.  One thing that may help is losing the fire brick on the inside and supporting your billet from the outside instead.  The fire brick can act as a heat sink. 

With the flux, keep your eye on it.  Once it starts to boil vigorously you should be good to go to set your welds.  Light but firm taps at first working from the center of the billet outwards to force out any flux.  Rinse and repeat 3 or 4 times before getting aggressive.

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Posted (edited)

I'll see if I can come up with something to get rid of the fire brick.

 

I guess I was thinking that the brick would make a smaller area that needed heating. I hadn't considered that the brick could absorb too much heat.

Edited by Daniel Sheets
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Posted (edited)

Two things I can think of right off the bat other than the brick- I ran a brick for a floor for a long time- but mine was half that thick. It took ten or more minutes... but I'd have that brick glowing orange/yellow. 

 

Try a coating in your forge. Itc is an IR coat thats rated to 5,000 °. It reflects heat back into your forge. Its a little pricey- but it'll help. I just re-lined my forge with last coat of this today....

 

Second- whats your regulator running at? You're getting a blue steady flame coming out in one of your pics. Venturi burner, or forced air? You might not have it turned up enough, it seems like you should have more "dragons breath" coming out... more fire, hotter burn.

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Edited by Welsh joel
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14 hours ago, Daniel Sheets said:

It's a Venturi burner. I couldn't tell you what the regulator is set on.

 

You know whats its adjustable to?

You want a 0-30 psi regulator for forge use generally.

I use a forced air burner, runs normally around 6psi or so. But to forge weld, I open it up to 10 or 12 psi.

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Posted (edited)
On 5/9/2021 at 10:32 PM, Daniel Sheets said:

I'll see if I can come up with something to get rid of the fire brick.

 

I guess I was thinking that the brick would make a smaller area that needed heating. I hadn't considered that the brick could absorb too much heat.

If it is soft firebrick it won't add appreciably to the heating load inside the forge.  However, reducing the inner forge volume without improving the forge liner's insulation doesn't really help.  Its a basic matter of heat into the forge versus heat out.  The heat entering is from the burner.  Heat exiting is from the forge skin and out the door/s.  Improved insulation decreases conduction through the forge liner, lowers the forge skin temperature (reducing conduction).  Reducing the forge skin temperature and the surface area, reduces the amount of heat lost to the environment by convection and to some extent radiation.  This is where ideas of reducing forge volume for efficiency come into play.  Putting in a brick reduces the interior volume without changing the skin surface area (though it may reduce the skin temperature on the bottom of the forge if it is a decent insulator).

 

A lot more heat is lot through the doors (both radiant heat and via the hot exhaust gasses).  This is one reason a forced air burner system can be more gas efficient.  You don't have to worry as much about back pressure so you can close your doors further.

 

San Mai is tricky, but not that hard once you are familiar with forge welding.  As usual, grind your weld surfaces clean, flux the billet immediately once it starts to show any color, and tap relatively lightly to set your weld once the flux is bubbling vigorously.  Don't forge out the blade till the weld is set and try to use steel that is at least 1/4" thick.  I'd keep a moderate billet size for your first few to make things easier on yourself.  Once you get the forge weld down then you only have to worry about keeping the core centered, warping in heat treatment, and the core cracking during the quench.

 

Enjoy...

Edited by Dan Hertzson
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